Is the world coming to an end?

[Nick Sabalausky]

"Don" <nospam at nospam.com> wrote in message 
news:inf4hj$3mg$1 at digitalmars.com...
> Nick Sabalausky wrote:
>> "spir" <denis.spir at gmail.com> wrote in message 
>> news:mailman.3141.1301915290.4748.digitalmars-d at puremagic.com...
>>> On 04/04/2011 07:26 AM, Nick Sabalausky wrote:
>>>> As far as LDC2, LLVM's uselessness on windows is a bit of a showstopper 
>>>> for
>>>> many people. And the LLVM project doesn't appear to be interested in 
>>>> doing
>>>> much about it. (Note I didn't say they *aren't* interested in getting 
>>>> it
>>>> working. That's not something I could even pretend to know. I'm just 
>>>> saying
>>>> that, at the very least, it *looks* like they don't care. And, for 
>>>> better or
>>>> worse, perception does count for a lot.)
>>> Yop, too bad. Else, LLVM could be the one target of choice for many PL's 
>>> "reference" implementation. I'd like to know rationales.
>>>
>>
>> AIUI, the standard explanation is that exception support on Windows 
>> requires SEH which is covered by a patent owned by Borland/Microsoft. But 
>> I have a hard time buying that explanation because non-MS compilers like 
>> GCC and DMC support exceptions on windows just fine - so why not LLVM, 
>> too?
>
> AFAICT, that explanation is absolute bollocks.
>
> SEH is *not* covered by a patent. The Borland patent that people talk 
> about refers to a particular implementation detail which is a workaround 
> for an absolutely horrific Microsoft bug.
> The idea is to use the exception handler pointer (which is in thread-local 
> storage(TLS)) to track which exception table to use.
> Instead of pointing to your exception handler, it points to a thunk (one 
> for each try block) which sets a pointer to the try block table, then the 
> exception handler.
> The reason for doing this, is that you need a TLS slot to store which try 
> block you're in.
> Unfortunately, Windows' thread local storage is hopelessly broken for 
> DLLs. The exception handler pointer is just about the only TLS slot 
> guaranteed to be available, so it allows you to escape the bug.
>

Interesting. (And could be another reason we need to get the DDL project up 
and running again :) )

> Now since the idea is just a straightforward application of thunks, I 
> wonder if it really satisfies the patent requirement for non-obviousness.
>
> But regardless, for D, Rainer has put code into druntime which fixes the 
> bug! So actually a D implementation can use any thread-local slot.
> <g>

Does that mean LLVM doesn't need exception support on Windows in order for 
LDC to support exceptions on windows?